Synopsis The pilot, four passengers, and a dog departed from Kimberley, British Columbia, at 1100mountain standard time (MST)(1) in the Aerospatiale AS 350BA helicopter (serial number 2374), for a visual flight rules flight to an alpine hut located at 6,500 feet above sea level (asl) in the Purcell Mountains, 12 miles to the west of Kimberley. The helicopter did not return to Kimberley and a search was initiated at 1600. The helicopter was found shortly after the search began; it had struck terrain in Boulder Pass, 10 miles west of Kimberley, at an elevation of 7,900feet asl. All occupants sustained fatal injuries at impact, and the aircraft was substantially damaged. Other Factual Information The pilot was the owner of Mountain High Helicopters Limited. At the time of the accident he was the sole pilot flying the helicopter, the company's only aircraft. He was certified and qualified for the flight in accordance with existing regulations and was experienced on the Aerospatiale Eurocopter AS-350BA. He was not instrument rated and had very little instrument training. The pilot's most recent pilot proficiency check was conducted with a Transport Canada inspector on 5 November 1996; the inspector noted that the occurrence pilot was a capable pilot. The pilot was familiar with the Boulder Pass route to the alpine hut, having flown it many times in the past. Three groups were to be flown to the alpine hut for avalanche training by a tour operator. On the morning of the accident, the flight was delayed because of low cloud and poor visibility along the route. When the low cloud in the vicinity of Boulder Pass began to dissipate, the pilot and the members of the first group decided to make the first flight. The helicopter departed from Kimberley, with the passengers and their supplies, at 1100. The helicopter was expected to return at 1130. When it did not return on schedule, the tour operator's representative felt it was possible that the helicopter had arrived safely at the hut, and that the pilot had decided to wait for conditions to improve before making the return flight. The representative thus delayed reporting the helicopter as overdue. A high-frequency radio at the alpine hut normally permitted communication with the tour operator's base in Kimberley. This radio required scheduled maintenance, which the tour guide was to have begun once the helicopter arrived at the hut. This task would likely have taken several hours. A search for the missing helicopter was organized after the representative had waited a reasonable time for the radio maintenance to have been completed, and after the weather had improved enough to preclude the possibility that the flight delay was weather-related. The helicopter was found beside Boulder Pass by another local helicopter operator, just before nightfall. It had struck terrain at an elevation of 7,900 feet asl, 1,000 feet to the left of the centre of the pass, and 60 feet below the top of the obstructing peak. Based on wreckage deformation and occupant injury patterns, the helicopter's speed at impact was estimated to have been between 50-70 knots. The heading at impact was about 300 degrees magnetic, which is consistent with the track leading to the destination. The main rotor blades had made a slash in the snow, just before impact, while the helicopter was still airborne. From an analysis of this slash, the helicopter's attitude was estimated to have been nose-down, 40 degrees relative to the horizon and about 80 degrees relative to the steep terrain. The fuel tank was ruptured at impact and its contents spilled, so a precise weight and balance of the helicopter could not be established. However, based on calculations of the fuel load required for the return flight, including reserves, and on (estimated) occupant and cargo weights, the helicopter's centre of gravity and gross weight were computed to have been well within the allowable limits, and were considered normal for this type of flight. There is no official weather reporting facility close to Boulder Pass. At the time of the occurrence, the weather at the Cranbrook airport (22 miles east of the accident site) was as follows: ceiling estimated at 3,300 feet asl broken, visibility 25 miles with snow showers in the vicinity, temperature minus 4 degrees Celsius, dewpoint minus 14 degrees Celsius, wind 140degrees magnetic at 11 knots, and altimeter setting 30.12 inches of mercury. The outside air temperature at 7,900 feet asl was estimated to have been minus 15 degrees Celsius at the time of the accident. At 1100 on the day of the accident, a helicopter pilot flying at 7,500 feet asl through a mountain pass eight miles south of the accident site reported that the visibility was restricted to one-halfmile or less, in heavy snow showers. He also observed low cloud at higher elevations. The pilot's onboard global position system navigation equipment calculated a 40 knot east wind at his level. This strong wind caused blowing snow on the surface, which obscured terrain features. Visual reference with the ground was further restricted by low cloud and flat ambient light that tended to create whiteout conditions, particularly in areas above the tree-line, such as the accident site. Another witness, at the alpine hut, reported that around the time of the accident the wind was very strong and was blowing long plumes of snow off the surrounding mountain peaks. This witness could not establish the visibility or cloud conditions at Boulder Pass at the time of the accident. Whiteout is an atmospheric optical phenomenon in which the observer appears to be engulfed in a uniformly white glow. Neither shadows, nor horizon, nor clouds are discernible, and depth perception and orientation are lost. The wreckage was recovered and the airframe, engine, fuel control unit, transmission, drive train, flight controls, and control actuators were examined. No pre-impact mechanical deficiencies or defects with respect to this aircraft or its component parts were identified. There was evidence of torsional loading on the engine and rotor drive train components. This evidence included torsional deformation of the engine-to-main-rotor transmission drive shaft, and bursting of the tail rotor drive flexible coupling. There was substantial damage to the main rotor blades, all of which revealed compressive, mid-span buckling. The rotor head Flexstar arms and sleeves were severely damaged or completely fractured. The Turbomeca Arriel 1B engine, serial number 4275, was removed from the airframe and disassembled. Of particular note was a substantial 3.8 mm shift in the alignment marks on the module 05 muffcoupling nut. During assembly, the muffcoupling nut is installed with a torque of approximately 20 dekanewtons (about 89 foot pounds). After torquing, the assembler marks the assembly with a scribe line. If the engine experiences a substantial over-torque, as would happen with a rotor strike, the muffnut will tighten and the scribe lines will shift. This shift of the alignment marks, the torsional damage in the drive train, and the extent of rotor head damage are conclusive evidence the engine was producing power and driving the rotor systems when the main rotor blades struck the ground.